JPS61183475A - Improved dip plating method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improved dipping method for plating on ferrous, non-ferrous and other conductive substrates.

There are a number of prior art methods for electroplating and electroless or immersion plating of tin or tin alloys onto substrates. however.

Interest in electroless methods has been growing for several years due to environmental concerns and energy costs. However, the prior art immersion techniques have not been able to satisfactorily overcome one or more drawbacks, such as long process times, elimination of porosity in the individual coatings, or uneconomical working conditions. Some conventional methods require a permanent zinc undercoat of the substrate, as disclosed in US Pat. No. 4,405,665.

Although useful, this method does not produce a porosity-free coating 7 and is limited to plating zinc-coated surfaces.

Other conventional methods may be unsatisfactory for some applications because the folding coating contains other elements or monomers rather than pure soot. Examples of such prior art include U.S. Pat.
No. 971,861 and No. 4,194,915.

Further disadvantages of the prior art include porous or poorly adherent tin coatings.

In others, the thickness of the applied rasp coating is very limited. Many conventional methods require heating the immersion bath to relatively high temperatures to obtain economically viable precipitation rates. Some methods are only applicable to hydrogen embrittlement of the substrate, specific metals, or a narrow range of metal substrates.

Many previous attempts have still failed to produce heavy, pure, pore-free and smooth non-granular tin coatings with efficient deposition rates in a manner that is relatively easily controlled by hour wheels? The present invention is directed to providing such an electroless immersion method.

SUMMARY OF THE INVENTION The present invention describes the treatment of metals or other conductive substrates in baths consisting of stannous ions, strong mineral acids, and surfactants alone or in combination with water-soluble acrylates and aromatic aldehydes or ketones. This invention relates to a dipping method for quickly depositing a film.

The metallic zinc or zinc alloy is placed in the bath and acts as a catalyst so that the primary conductive contact between the zinc and the substrate to be coated causes the deposit of the zinc onto the substrate with a strong non-porous adhesion. It becomes effective.

As used in Komata, and to distinguish it from prior art methods, the contact or bond between the catalytic metal and the substrate does not require permanent adhesion, but is preferred. is a simple direct contact,
Alternatively, it is indirect temporary bonding via a tetraelectric medium.

Within the operable range of bath compositions and with the appropriate amount of metallic zinc supplied to the bath, the deposited film is free of pores and smooth with close adhesion to the substrate. It was discovered that The thickness of the coating produced by practicing the method of the invention is limited only by the working time and provides economically practical results.

The immersion bath has a composition range of the following ingredients: 5 to 70 grams of stannous ions per liter of water, 10 to 200 grams of a strong mineral acid such as sulfuric acid, and 10 to 10 grams of length per liter of water. It consists of a nonionic, cationic, zwitterionic or anionic surfactant containing an ethylene oxide bulk polymer component in the range of about 40%.

Each of these surfactants is 0.1 to 10.0 g.
A glossy, adhesive metal coating χ can be produced using a combination with a water-soluble acrylate in the range of 0.01 to 1.0/l and an aromatic aldehyde or ketone in the range of 0.01 to 1.0/1.

The metallic zinc or zinc alloy used may be in the form of a single piece or a plurality of pieces. Sizes range from powder or dust to small, thin plates or strips.

Alternatively, depending on the special purpose, large plates or blocks may also be included. The zinc is brought into conductive contact, directly or indirectly, with the substrates to be coated while they are immersed in the bath. This contact between the zinc and the substrate may be continuous during the working period or may include a number of intermittent contacts.

The operating temperature of the bath is 30 to 100'F (10 to 25
The operation is very conveniently carried out within the typical normal room temperature range.

The bath maintains a long lifespan (with regular replenishment) under typical use (with regular replenishment) and is stable in normal environments and ambient temperature ranges.

OBJECTS OF THE INVENTION The main object of the present invention is to provide an electroless dipping method for seamlessly coating tetraelectrical areas such that the coating is porosity-free, smooth, and adhesive. .

Another object of the invention is to provide independent flakes of metallic zinc which act as catalysts when brought into conductive contact with the substrate to be coated so that the deposition of the tin coating onto the substrate takes place effectively. Another object of the present invention is to provide a method of the type described above for use in a zinc alloy plating bath.

Another object of the invention is to provide a process of the above type in which the bath components are free of cyanogens or toxic metals or other highly undesirable environmental components.

A further object of the invention is that the bath can normally be operated at room temperature;
It is an object of the present invention to provide a process of the above-mentioned type which has a long useful life and in which the waste bath can be recycled in a relatively economical manner with respect to its residual metal content.

Still another object of the invention is that each and every coating is pure, i.e., free of alloys and other contaminants, and that the thickness of the coating is not limited for reasons other than practical and economical for a given application. It is an object of the present invention to provide a method of the type described above, which is qualitatively not limited.

Yet another object of the present invention is to provide a cohesive metal tin deposit by combining a water-soluble acrylate and an aromatic aldehyde or ketone with a surfactant in a bath to obtain a glossy tin coating. There is a particular thing.

Further objects and advantages of the present invention will become apparent from the following description which clearly describes preferred embodiments and examples of the invention.

SUMMARY OF THE INVENTION The present invention relates to an improved electroless tin dip deposition method for depositing pure tin coatings on ferrous or non-ferrous metals and other conductive substrates.

While the substrate to be coated and the catalyst metal consisting of zinc or zinc alloy are both immersed in the bath.

A sword that is in direct or indirect conductive contact.

It has been found that a heavy, non-porous coating can be applied to such substrates. Therefore, unlike conventional methods of this type, it is not necessary to apply a zinc or other metal undercoat to the substrate in order to obtain a topcoat of pure chives. Furthermore, there is no need to apply mechanical blows χ to make the film adhesive. The term "zinc" used here also includes zinc alloys.

The conductive contact required in the invention may be by direct metal-to-metal contact between the zinc and the substrate, or by other metal pieces, such as metal wires or metal strips, in contact with both the zinc and the substrate. This can effectively be done by indirect conductive contact through a conductive intermediary. Ding is deposited only as long as there is a conductive contact between the substrate and the zinc.

In some applications, conductive contact is made in an intermittent, random manner, such as by rolling the zinc strip and the small metal member to be coated in a bath, thereby creating a random, intermittent electrical conduction between the base member and the zinc. It is desirable that contact be made.

The bath compositions addressed by the present invention have the advantage of not using cyanide or toxic metals or other environmentally harmful components that create difficult processing or disposal problems. According to the invention, the immersion plating bath has the following composition. ethylene oxide bulk polymer component in an amount ranging from 5 to 70 grams per liter of water, 10 to 200 grams of a strong mineral acid, preferably sulfuric acid, and a length ranging from 10 to 40 percent. With taste.

or non-ionic, zwitterionic, containing in combination with water-soluble acrylates and aromatic aldehydes or ketones;
0.1 to 10 grams of cationic or anionic surfactant.

The concentration of mineral acid must be sufficiently high to ensure that stannous is present in the solution and to prevent the formation of insoluble tin hydroxy- or oxy-complexes which are easily removed from the solution. No.

Preferred acid concentrations for the present invention are between about 30 and 80 grams per liter of water.

For the purposes of the present invention, a smooth, pore-free coating rather than a single grain is desirable. Generally, higher concentration levels of stannous ions used in solution will increase the rate of precipitation within the ranges disclosed herein. Lower concentration levels of stannous ions require longer soak times to ensure a porosity-free tin coating. The preferred range of stannous ions in the present invention is between about 12 and 20 grams stannous ions per liter of water; within this preferred range, smooth, non-granular, and pore-free coatings are obtained in relatively short working times. Very good to very good results have been obtained.

A preferred nonionic surfactant is nonylphenoxy-
It is poly(ethyleneoxy)ethanol. Preferably, the surfactant is used at a concentration of 0 grams W:JO,S per liter of water. The preferred molecular weight range for this nonionic surfactant is about 484 to 10
It is between 000 and 000.

The immersion plating baths used in the practice of this invention are also within the typical ambient temperature range of approximately 30 to 110 degrees Fahrenheit (110 degrees Fahrenheit).
0° to 45°C). The precipitation rate of cloves increases with temperature, but at about 100'F (58°C)
Above this, it becomes difficult to maintain the solubility of stannous ions in the bath. Bath warm air is below 100 to 110 (5
(8° to 45°C), the tendency for the formation of insoluble hydroxy-tiny compounds or oxy-tiny complexes increases markedly, leading to severe and significant losses of stannous ions. become. Therefore, it is not necessary, and generally undesirable, to heat the bath to relatively high temperatures, as is required in conventional methods.

The bath is stable under typical replenishment conditions over a relatively long period of use, over 6 months. A new bath must be used when the concentration of zinc ions in the solution approaches the saturation point. The bath allows relatively high levels of zinc ions in the liquid. The present invention still works well with 10 grams/liter and more of zinc ion in solution. The concentration of the main components of the bath can be easily controlled by titration.

According to the invention, once the coating is deposited to a minimum thickness, standard General Motors test method 9074-
A pure dust coating, which is free of pores as measured by P, can be deposited. The bath composition is for pores or the like;
It also has excellent coverage over a distance of 12 inches (305 mm) or more as measured from the point of conductive contact between the substrate and the zinc catalytic metal.

The basic preliminary work of the invention does not limit the thickness t of the tin coating. As long as there are enough stannous ions and enough zinc metal left in the bath, the zinc ions will remain on the substrate until the concentration of zinc ions in the solution approaches saturation and/or until the bath is depleted of stannous ions. It continues to precipitate.

Corrosion testing of the fastener coatings conducted by the inventor showed that they were equivalent to cadmium plated fasteners. Tensile torque tests have shown that the edge coatings applied in accordance with the present invention are equivalent to standard cadmium plus wax coatings on fasteners.

Selective coating of individual coatings is easily and accurately applied to the substrate provided by an insulating mask or similar means, since the coating is simply deposited by making conductive contact with the zinc. Since tin tin is approved by the FDA, the use of tin coating on food containers using the present invention would be highly desirable.

It has been found that preconditioning of the metal substrate to be coated for the purposes of the present invention can be accomplished using current conventional processes used to prepare metals applied to corrosion resistant phosphate coatings. .

Exemplary embodiments of the invention are described below.

Example 1 A sheet of iron substrate was immersed in a bath at room temperature (75'F (24C)). Four metallic zinc strips were tied to opposite edges of the iron substrate by copper wire stretched through holes drilled in the substrate and the zinc strips.

The substrate is pre-prepared by the usual cleaning and descaling steps as cited above. These processes are alkaline cleaning followed by water washing.

It consisted of alkaline descaling followed by water washing, and finally organic acid treatment and water washing. The substrate was then subjected to a coating process.

The composition of the immersion bath was as follows.

Stannous sulfate 27 1/1 Sulfuric acid 70 g/I IGEPALC06301g/1 (IGEPAL GO630 is manufactured by GAF Corpora
Water (which is the trade name of nonylphenoxy-poly(etheneoxy)ethanol commercially available from tion)
The remaining iron substrate and zinc were immersed in the bath for 5 minutes. A smooth, adherent, non-porous coating was deposited on the substrate and was measured at 1142 mg/ft2 (125 mg/di) on the substrate surface, with an average thickness of 1.67 microns.

Example 2 Using the same conditions and steps as described in Example 1, a similar iron substrate and zinc catalyst strip was immersed in the bath for 1 minute. A similar tin film was deposited on the substrate, but with an average thickness of 0.
295mg/ft” (5
1.5 my/dm”).

Using the same preparation steps, bath composition, and bath temperature, multiple metal fasteners, screws, and bolts were placed together with several strips of hot-dipped steel in a multi-perforated rotating barrel. The barrel is then dipped into the bath and rotated for 5
was allowed to perform random mixing and contact between the various parts and the hot-dipped steel strip for minutes. After this 5 minute soak.

The barrel was removed and the fasteners, screws and bolts were rinsed and then soaked in a calcium chromate solution for 1 minute.

Visual inspection revealed a relatively heavy, smooth coating on each component. The parts are dried.

Tecty L 605 was oiled and then subjected to salt spray. After 168 hours, inspection of these parts showed no signs of rust.

Example G Al 4 Using the same preparatory steps, bath temperature, stannous ion content and mineral acid content, 109/1. Surfactant combinations were prepared with concentrations ranging from 0 g/l and 0.1 to 101/l. Both iron and other substrates were brought into intermittent contact with the zinc catalyzed metal immersed in the bath for 5 minutes and coated with a very shiny and adherent tin deposit.

Each of the resulting coatings obtained in Examples 1, 2.5 and 4 was tested using General Motors test method GM9079.
-P and found to be free of pores.

This test method is the generally accepted standard for measuring the integrity of coatings on ferrous substrates in the automotive industry.

The influence of operating parameters of bath concentration on the coating process has been studied.

A complete study of the molecular weight range of water-soluble preferred surfactants covering the entire range of the IGEPAL CO series of surfactants is available from GAF Corporation.

In this study, the preferred surfactant, nonylphenoxy-poly(etheneoxy)ethanol, was
It has been shown that a lower molecular weight range of 0.00 is preferred in connection with obtaining higher efficiency of zinc catalytic metal.

In this lower molecular weight range, the coating that is also deposited on the zinc during this process has good adhesion, but becomes more porous. The method of the present invention uses zinc ions Z in a solution.
Since this requires replacement, a sufficient amount of zinc metal surface area is required to maintain sufficient precipitation coupling Z without refeeding to a new catalyst metal bibath. Higher molecular weight ranges tend to reduce the porosity of the film deposited on zinc. This porosity tends to more easily limit the useful life t of the initial zinc catalyst metal in the bath.

However, the nature and proportion of the coating deposited on the substrate is not significantly affected as long as sufficient exposed metallic zinc catalyst surface area is available to assist in displacing zinc ions.

The effect of the concentration of this preferred surfactant was studied and it was found that the lower the lower end of the disclosed range, the more granular and porous the tin deposition on the zinc catalyst tends to be. This is desirable for the present invention because the exposed metallic zinc surface area is more dense and can remain for longer periods of time, thus increasing the useful life of the zinc catalyst according to the invention.

Furthermore, it should be noted that the surfactants used in accordance with the present invention are those that significantly control the rate of precipitation of dust. If this type of surfactant is not in sufficient concentration, it tends to rapidly deposit on the zinc catalyst metal or substrate in the form of a poorly textured, non-adhesive muddy coating. This coating is useless for the purpose of the invention and represents a waste of expensive stannous ions.

The effect of sulfuric acid concentration was studied, and the concentration range was determined by the amount required to prevent the formation of insoluble tin hydroxy or oxycomplexes in relation to the amount of stannous ions in solution. It was found that this is possible. 10
Acid concentration ranges above 0 g/l are sufficient to keep practical higher concentration limits of stannous ions in solution.

Acid concentration did not appear to have a noticeable effect on the properties of the deposits on the substrate within the concentration range shown here.

Studies of the effect of stannous ion concentrations in the range of 15 to 70 grams F per liter of water have revealed that as the concentration of stannous ions increases, the rate of deposition of the tin film increases.

The lower the concentration value within the indicated range, the proportionally longer it will take to obtain a pore-free coating. It has been found that once the coating thickness reaches about 0.025 mils (0.58 microns), a porosity-free coating is obtained.

The stannous ions cannot be maintained at concentrations greater than about 100 g/1. At such a high concentration, stannous ions become oxy-compounds of tin and/or hydroxide of tin and precipitate out of the solution.

To obtain the results7 specifically required for a given application,
It must be pointed out that other than the specific embodiments shown here, different means may be used to make the necessary electrically conductive contact between the zinc catalyst and the substrate to be coated.

In this method, the coating deposited on the substrate to be coated tends to be slightly thicker at points closest to the electrical contact points between the zinc and the substrate.

This is referred to as the "wedge J effect."However, if appropriate for a given application, multiple fixed contact points 7 or a perforated barrel as described in Example 5 may be used. By providing frequent random and intermittent contact 7, such as rolling in the material, this can be minimized and a more uniform thickness of the coating can be applied.

Furthermore, a means of effecting the necessary contact between the substrate and the zinc is obtained by placing the part 7 to be coated into a perforated zinc barrel.

The barrel of zinc immersed together with the green part can then be rotated to provide frequent random and intermittent contact 7 between the part to be coated and the zinc barrel.

In addition to other applications shown herein, the method of the invention is used for selective coating on printed circuit boards, high speed coating on wire, and aluminum pistons and other friction bearing components to reduce friction. It can also be advantageously used for tin coating.

Furthermore, research on the properties of surfactants that work to effectively control the precipitation rate of stannous ions on the surface of the member to be coated has shown that ethylene oxide or Other surfactants, including bulk polymers of propylene oxide, have been shown to be excellent candidates for use in the present invention.

Of the many such options and their various combinations, only a few have been tested and have shown good results, with only 1 to 5 being found.

Preferred surfactants disclosed in the present invention further include one or more of the group consisting of alkylarylphenol-poly(ethyleneoxy)ethanol having the general formula R2-C)I2-0]R2. It can be defined as above. However, an alkyl chain having a length of 6 to 20 carbon atoms or an alkyl chain having a length of 1 to 20 carbon atoms is also a realkylphenol, and R2 is hydrogen.

In addition, a porosity-free, smooth surface coating with strong adhesion to the substrate can also be obtained in a bath containing a surfactant as described herein and a water-soluble acrylate and an aromatic aldehyde or ketone. It was discovered that This combination in a bath as described in Example 4 resulted in a single coating as obtained in the previous example.

However, the coating is more glossy. Or even had a clearer appearance.

Preferred water-soluble acrylates appear to be salts of methacrylate polymers such as ammonium methacrylate, although others should also give good results. Similarly preferred aromatic aldehydes or ketones are nandaldehyde or naphthyl ketone, although other similar ratios are expected to yield similar results.

It should also be noted that the method of the present invention differs from prior art electroless contact methods in that the substrate on which each coating is deposited may be more or less base than the starting zinc or catalytic metal. It is.

In view of the foregoing, the present invention represents a very significant advance in the art and provides a novel method of immersion plating that provides many benefits not found in the teachings of the prior art. It should be easy to see that.

(Name to remove)

Claims (11)

[Claims] (1) (a) About 3 to 70 grams of stannous ions per liter of water. (b) a strong mineral acid of about 10 to 200 grams per liter of water, the concentration of the acid being sufficient to retain liquid stannous ions in the bath; and (c) a Coating in a bath with a surfactant content of 0.1 to 10 grams, which functionally controls the precipitation rate of stannous ions in the acid bath environment, to obtain an adherent, non-porous tin coating. 1. A method for coating a conductive substrate with tin, comprising the step of dipping the substrate to be tinned and one or more pieces of zinc metal. (2) The surfactant has a length R_1 of 6 to 20
is an alkyl chain consisting of carbon atoms or has a length of 1
from alkylarylphenol-poly(ethyleneoxy)ethanol having an alkyl chain of from 1 to 20 carbon atoms and essentially having the general formula R_1[CH_2-CH_2-O]R_2 when R_2 is hydrogen; The method according to claim 1, characterized in that one or more of the following are obtained from the group consisting of: (3) the surfactant has a length of essentially 10 to 40
Process according to claim 1, characterized in that the surfactant is one or more surfactants from the group consisting of bulk polymeric components of ethylene oxide or propylene oxide within the unit range. (4) The bath further comprises water-soluble acrylates and one or more components from the group consisting essentially of aromatic aldehydes and aromatic ketones. The method described in section 1). (5) Claim (4), wherein the water-soluble acrylate is a salt of a methacrylate monomer.
The method described in section. (6) A process according to claim 4, characterized in that the aromatic aldehyde or ketone is one or a mixture of components obtained essentially from the group consisting of naphthaldehyde and naphthyl ketone. . (7) The mineral acid content in the bath is between 30 and 8 per liter of water.
Process according to claim 4, characterized in that the concentration of sulfuric acid is 0 grams. (8) The concentration of stannous ions is approximately 12 per liter of water.
A method according to claim 4, characterized in that the amount is between 20 grams and 20 grams. (9) While immersed in the bath, the interaction between the substrate to be coated and the metallic zinc is made effective so that conductive contact between the substrate and the zinc is randomly and intermittent. 4. A method according to claim 4, characterized in that the method is carried out in a repeatable manner. (10) The substrate to be coated consists of a plurality of respective parts, and said substrate parts and said plurality of metallic zinc pieces are arranged in said bath in such a way that random conductive contact is induced between the blank parts and the zinc. A method according to claim 9, characterized in that it is rolled. (11) the metallic zinc is generally in the form of a barrel-like perforated container, the substrates to be coated are placed in the container, and the container is immersed and rotated in the bath; The method according to claim (9), characterized in that: